A four-quadrant detector is commonly used for determining position of a projected optical beam in an optical apparatus, and providing signals that are used to drive one or more movable optical components for steering the beam. One example of a laser beam to be steered is an output beam from a laser.
A laser output beam may be subject to variations in its direction and shape as a result of changes in parameters of the output beam such as output power, pulse width, pulse repetition frequency, and the like. The shape of a laser beam can be modified by passing it through an optical system including one or more optical elements that have different optical power in different transverse optical axes. Variations in the shape of the output beam can be corrected by moving one or more elements of the optical system with respect to another to change the magnification of the system in one of the axes in preference to the other. It would be advantageous to derive information regarding the position and shape of a laser output beam from a single quadrant detector.